2009 Kenworth W900 Cat C-13 Acert Oil Pressure Gauge Drops Out

2009 Kenworth W900 Cat C-13 Acert
The Oil Pressure Gauge keeps dropping out. I have replaced the sending unit, checked that it does have oil pressure with a manual gauge, checked the wiring, replaced ECM, replace Body ECU, tried a known good gauge, Y'ed in to the EOP sending unit and watched as it showed proper voltages, but all too no avail. After the engine runs for a few minutes the gauge will bottom out and that's it.

Any help would be appreciated.